I'm using Lightroom Mobile for Android on a Galaxy S6 and have ~2.2k photos on my phone's Gallery. I added all of these photos to Lightroom and proceeded to wait for several hours while it added them all. In the end, it imported all but about ~50 of the photos. No matter what I tried, I can not get these last 50 photos to import. I have tried:

Many different permutations of trying to import the photos

Force closing the Lightroom app

Deleting the cache for Lightroom

Deleting the data for the Lightroom app

Uninstalling and reinstalling the Lightroom app

While trying these things, ~850 of the photos synced to the Lightroom Cloud. And now after reinstalling, the following things are worth noting:

When logging back in to my account in the Lightroom Mobile app, it adds the ~850 photos that were synced to the Lightroom Cloud back into the Lightroom Mobile library

When I try to import the ~2.2k photos from my phone's Gallery back into Lightroom Mobile, it quickly goes through all of the photos without adding any of them (presumably because it thinks they're all in the library already?)

The Lightroom Mobile app tells me that it's trying to sync ~1400 photos to the Lightroom Cloud (even though there are only ~850 photos in the Lightroom Mobile library (presumably this is because it's trying to sync the remainder of the ~2.2k photos originally imported which aren't actually in the library anymore))

Soo.. what do I do next? I'd like to get all of the photos imported into the mobile library and uploaded to the cloud.

I was having some problems importing photos from certain Android folders into Lightroom (it just said "failed to import"). Upon some trial and error, I realized it failed if the folder's name had an apostrophe in it. So I removed those apostrophes from those folder names and it worked as it should. Might be unrelated to your problem but check your directories.